Since Acquired Immune Deficiency Syndrome was first described in 1981, about 33,000 people have been identified as having AIDS and about 18,000 have died of the disease in the U.S. It has been estimated by the Center for Disease Control, U.S. Public Health Services, that in this country 1.5 million people have been exposed to the AIDS virus (Human Immunodeficiency Virus, HIV) and that by 1991, 5 million people will have been infected. Although there are groups identified as being at particularly high risk of developing the disease (e.g., homosexuals, intravenous drug users), increasing proportions of the infected people belong to groups not seen as high risk (e.g., heterosexuals, children, newborns). Recently, the World Health Organization warned that as many as 10 million people world-wide are infected with the AIDS virus and that in 10 years, as many as 100 million will be infected. It is not surprising that many health agencies around the world predict that AIDS will be the most common life threatening disease in the last part of this century and the beginning of the twenty first century.
When people are first infected with HIV, they develop antibodies against the virus. Most infected individuals remain symptom-free, although they continue to harbor the virus. Data have suggested that from 20-30% of those infected with HIV will develop AIDS and that of those who do, about 50% will die within 5 years. More recent studies have indicated that up to 75% will develop AIDS in 7 years. An even larger proportion of those infected will develop less severe immunodeficiency-related symptoms, referred to as AIDS-related complexes (ARC). Many patients with ARC eventually develop AIDS.
The AIDS virus is an unusual virus. It infects and destroys the CD4 antigen positive (CD4+) helper/inducer T cells, an important subpopulation of immunocytes involved in the regulation of immune responses. It has been shown that a very reliable indicator of the progression of infected individuals from symptom-free status, to ARC and then to clinical AIDS is a decrease in the number of CD4+ cells and the ratio of CD4+ to CD8+ cells. Thus, physicians generally prescribe assays to evaluate the immune status of individuals identified as seropositive or HIV-infected. Even individuals already determined to have ARC or AIDS are routinely monitored, by the lymphocyte subset determination, for disease staging purposes or for monitoring the results of therapeutic treatments.
Currently, the lymphocyte subsets are usually determined by fluorescence flow cytometric methods. This method requires costly equipment and specially-trained medical technicians. Although many major hospitals have set up facilities for carrying out these methods, most clinical laboratories, small hospitals, and doctors' offices find it difficult to do so. In economically underdeveloped countries, where AIDS is endemic, performing flow cytometry routinely is almost impossible because of the prohibitive expense and the technical capabilities necessary. A simpler, more easily conducted, less costly method of lymphocyte subset determination would be very valuable in the diagnosis and monitoring of AIDS, as well as other diseases.